Insulating materials and method of preparing insulating materials



Nov. 13, 1934- M, c. LEWIS ET AL 1,980,413

INSULATING MATERIALS AND METHOD OF* PREPARNG INSULATING MATERIALS FiledAug. 24, 1930 2 Sheets-Sheet l Nov. 13, 1934. M. c LEWIS ET ALINSULATING MATERIALS AND METHOD OF PREPARING INSULATING MATERIALS FiledAug. 24, 1930 2 Sheets-Sheet 2 fil. ////7 GUN w Patented Nov. 13, i9341,980,413

UNITED STATES PATENT OFFICE INSULATING MATERIALS AND MIETHOD F PREPARINGINSULATING MATERIALS Mark C. Lewis, Cranford, N. J., and Alger M.

Lynn, Oak Park, Ill., assignors to Western Electric Company,Incorporated, New York, N. Y., 'a corporation of New York ApplicationAugust 24, 1929, Serial No. 388,251

24 Claims. (Cl. 8 2) This invention relates generally to insulatingments spun into a strand, such as is known as materials and methods ofpreparing insulating tussah spun silk. materials and more particularlyto iibrous in- In the degumming of silk by one commercial sulatingmaterials, such as silks, and methods of method the usual steps employedare to subject preparing them, Y the silk to a hot solution containingan alkaline 60 The characteristics of many insulating masubstance, suchas soap, caustic soda, soda ash, terials vary with the conditions underwhich sodium phosphate or the potassium compounds they are used and itis sometimes necessary to corresponding to these sodium compounds. thenemploy an excess of certain insulating materials to wash the thustreated silk with water, then over the amount required for normalconditions with a dilute solution oi sulphuric acid, and 65 in order toprovide adequate insulation under finally to wash the silk several moretimes with unusual conditions. For example, the electrical water.characteristics of the usual commercial insulat- Another commercialmethod of degumming ing silks, such as are employed to insulate elecspunsilk is to treat the silk with hydrochloric n trical conductors, varynoticeably with variations acid to remove soluble impurities, then totreat 70 in humidity, and in order to insure the desired the silk with adegumming agent, such as one of electrical characteristics under allconditions, it those enumerated hereinabove, and finally to is necessarywhen using such insulating silks to wash the silk a number of times withwater.

provide not only the amount oi silk required for Experiments have shownthat when silk is deordinary conditions, but also an additional gummedby the usual commercial methods the 76 quantity of the silk which issuiilcient to give silk may contain small quantities of impurities therequired characteristics under conditions of introduced in the degummingprocess which may high humidity. comprise compounds having either acidor alka The economic losses, such as increased costs line reactions, Theusual impurities present in 26 of materials, additional labor, loss oftime., wear degummed silk are sulphuric acid in the case of 80 onmachinery, investments in additional macontinuous filament silk andalkaline compounds chinery; etc., resulting from using such insulatingin the case of spun silk. Since all of these mamaterials are readilyapparent, and furthermore terials are readily ionizable in water,insulating the electrical characteristics oi conductors insilks whichcontain them vary in electrical char- 30 sulated with such materials arealso likely to be acteristics in accordance with the amount of mois- 85irregular. ture present therein, and the electrical charac- Thisinvention has for its objects the provision teristics of such insulatingsilks are likely to be of insulating material having substantiallyuniseriously affected under conditions oi high huiorm characteristicsunder varying conditions of midity.

service, and the provision of simple, expeditious, insulating silkembodying the invention, from 90 and economical methods of preparingsuch mawhich such ionizable substances have been reterials. moved andwhich in consequence has substan- Insulating materials embodying theinvention tially constant electrical characteristics under may beprepared in accordance with the invenvarying conditions oi service, maybe produced tion by subjecting a fibrous material, such `as ininaccordance with the methods embodying the 95 sulating silk, to aplurality oi' hot washing fluids invention which will now be described.under pressure, at least one oi the fluids includ- The methods embodyingthe invention may be ing a reagent capable of neutralizing impuritiesmost effectively practiced by means of apparatus in the insulatingmaterial, and the remaining of the type o1' the so-called Franklindyeing fluids comprising water. machine disclosed in the accompanyingdraw- 100 In the preparation oi' insulating silks by the ings, in whichusual methods one of the steps employed is that Fig. 1 is anelevational. view partly broken away of degumming the silk in order toremove the of a. material treating apparatus; gum (serecin) and otherextraneous materials Fig. 2 is a plan view thereof, and

which may be present, from the'silk'bre itself. Fig. 3 is a graphshowing the electric charac- 105 The degumming proces's varies with thediiierent teristics of treated and untreated insulating silks. kinds ofsilk treated, and depends upon'whether Referring now to the drawings, inwhich like the silk treated is a continuous filament silk, such numeralsdesignate like parts throughout the as is known as tussah tram silk, orwhether the several views, the numeral 10 designates a cylin- Silk iSmade 0f a Dumber 0f discontinuous 111%- drical vessel having a removablecover 11 which 110 Vwhich permit the ow of uid from the chamber 17 intothe chamber 18, and-the' partition 15 is provided with a larger centralopening 21, which leads into a pipe k23, extending through the chamber19and through the bottom o! the vessel 10 where it'connects with a pipe24. The partition 15A is provided with a plurality or openings 26.-26,which are in alignmentnwith corresponding openings in the'partition14".through which openings hollow, perforated spires 27-27 extend, so asto permit the H ow of a fluid to and from the chambers 17 and 19 withoutthe "fluid owing into the chamber 18.

'I'he cover 11 is provided with a plurality of spring pressed plungers29-29, one for each of the spindles 27-27 and in alignment with thesespindles, lso as to exert pressure upon packages of insulating silk30-30 wound upon springs 31-31 and positioned upon the spindles 27-27 inthe mannerclearly illustrated in Fig. 1. The plungers 29--29 alsoprevent thefluid which flows through the openings inthe spindles 27 27from passing out of the top of the channel surrounding the spindlesformed by the springs 31-31 and the silk wound thereon, and the plungersthereby cause the liquidto iiow through the silk under pressure so. asto wash the silk.

The bottom of the vessel 10 has an openingl33 therein, at which point apipe 34 is connected so as to convey fluid to and from the chamber 19.

`The pipes 24 and 34 lead from the vessel 10 to a reversing valve 36from which pipes 37 and 38 lead to the inlet and outlet portsrespectively of a centrifugal pump 40 driven by an electric motor 41. Anexpansion tank 43 is positioned .abovethe pump 40 and a drain pipe 44leads from the bottom of the tank 43 to the pipe 37 so as to dischargethe contentsof the expansion tank into the-,centrifugal pump 40. Theexpansion tank 43 is also provided with an overflow pipe 46 leading to awaste discharge system, of any suitable type (not shown), -to preventthe contents of the expansion tank from overflowing into the room'.

lSteam inlet pipes 51 and 52 are provided below the vessel 10 to permitthe introductionof steam into the pipes 24 and 34, respectively, and thevessel 10 is provided with pressure gauges 47 and 48 which indicate thepressure within the chambers 17 and 19, respectively. The vessel 10 isalso 'provided with an overflow pipe 49 leading into the expansion tank43, in which pipe is positioned athermometer 50, by means of which thetemperature within the chamber 17 may be ascertained and a valve 54 isprovided to permit the iiow of uid through the pipe 49 when desired. Adrain valve 53 is also provided adjacent the reversing valve 36 to drainthe fluid from the apparatus into a Waste discharge system (not shown)whenever it is desirable.

The operationv oi the apparatus is as follows:

The cover 11 is removed from the vessel 10 and a plurality of packagesof silk 30-30 are -will enter 'the vessel 10 through the pipe 24 and Thepump 40 is then started, whereupon the washing fluid is pumped from thetank 43 through the pipe 38 through the reversing valve 36, through thepipe 34 and into the chamber 19 in the bottom of the vessel 10. The uidpasses from the chamber 19 up through the spindles 27--27, out throughthe packages oi silk 30,-30, down through the spaces between thepackages, through the openings 20-20 in the false bottom 14 and throughthe opening 21 in the false bot- 85 ,tom 15, then `through the pipes 23and 24-back through the reversing valve 36, through the pipe 37 and tothe centrifugal pump 40, whichthen recirculates the fluid through theapparatus. Whenever it is desired Ato change the direction of the flowof the washing uid the reversing valve 36 is actuatedto connect the pipe24 to theoutlet port of the pump 40 and to connect the pipe 34 to theinlet port of the pump so that the liquid leave the vessel through thepipe y34 in a path which is directly opposite that describedhereinabove. When it is desired to heat the iluid being circulatedthrough the apparatus, steam may be introduced into the fluid throughthe pipes 51 and 52 for that purpose. l l f The above describedapparatus may be employed to practice a number of methods embodying theinvention, and in order that the invention may be clearly understood onespecic method embodying the invention will now be described. Y.

In practicing this method, silk spun into strands is wound upon thesprings 31-31, each spring carrying about .75 pound of silk, and theresulting packages `are positioned in the vessel 10l over the'spindl27-27 in the manner dey scribed hereinbefore. Water at a temperature ofabout 130 F. is then introduced into the expanson tank 43 until about1.7 gallons of water 115 per poundof silk has been introduced therein;and the circulating pump 40 is then started, whereupon the water iscaused to circulate under pressure through the .silk in thel mannerwhich' has already been described. A quantity of acetic 120 acidequivalent to about, .'13- pound of 100% acetic acid per pound of silkis then introduced into the expansion tank 43 and forms a solution withthe water therein, which is capable of neutralizing the alkalineimpurities, such as degumming agents, which are present in the silk.Steam is then admitted through the pipes 51 and 52 into the streams ofwashing uid passing to and from the vessel 10, which rapidly heats thesolution to a temperatureof about 200 F. The 130 hot solution iscirculated through the silk for about twenty minutes, during whichttlmethe direction of ow of the iiuid is changed twice by v.

actuating the reversing valve 36; thenzthe-upump f Y 40 is stopped andthe washing iluid' is drained 135 from the apparatus through thedrainfvalye/SS.'

Water at a temperature of about v F, is thenagain introduced into theexpansion-tank 40.; `and the above steps, except the addition v of,acetic l acid, are repeated. The silk is washed a'- num1140 ber of timeswith hot water under pressure-` the manner just described, in order towashthesilk free of ionizable-materials, the numl'aeijv oi?v washesdepending upon the amount of impuri-A ties in the silk. Experiments haveshown that a process including one washing with a hot acetic 1 1 acidsolution followed by four Vwashingsfvvith hot water gives verysatisfactory results.v

After the silk has been'subjected tog-the i1$ribed washing steps, it isthen dredfbyiirst {15(1- centrifuging it and then heating it in a hotair drier at a temperature sufllciently high to evaporate the waterretained by the silk and to volatilize the acetic acid retained therein.Any acetic acid which remains on the silk after the -drying operationgradually volatilizes until substantially all of the acetic aciddisappears, and in' any event the quantity of acetc acid retained on thesilk is so small and the acetic acid is such a weakly ionizablesubstance that it does not materially alter the electricalcharacteristics of the silk under conditions of high humidity.

It is, of course, to be understood that the method just described ismerely an example of numerous methods embodying the invention which maybe employed and various modications may be made without departing fromthe spirit'and scope of the invention. For example, when the silk hasbeen degummed with soap it is sometimes desirable to first subject theslk to hot water under pressure, then to employ a hot washing uidcontaining acetic acid, and nally to 'wash the silk several times withhot jwater. Furthermore, the number of washing steps employing either`acetic acid or water may be varied in accordance with the amount ofimpurities present in thefsilk.4 If the silk contains a large amount ofalkaline materials, the step "of washing the .silk with yan acetic acidsolution may be ref-'- heated; or if the silk contains only asmallquantity of' impurities, the acetic acid washing stepv may be omittedentirely; or one acetic acid wash maybe employed and followed by lessthan four water washes. The quantity of acetic used in any one washingstep may also be variedinaccordance with the amount of alkalinematerials in the'silk-being treated.

Nor-is it necessary to use only acetic acid as a reagent forneutralizing the alkaline impurities in the silk, for any 'weaklyionizable acid or mixture of acids may be employed Ior'this purpose. Thevolatile fatty acids are preferred, however, because they do not ionizestrongly and because they either decompose or vaporize during the dryingof the silk, or on standing after the silk is d'ied, without leavingresidues which act as electrical conductors. Among the `acids whichl maybe used either alone or in combinations are formic, acetic, propionic,lactic, oxalic, tartaric, citric, carbonio and malic.

It is, of course, not essential in all cases to employ an 'acid solutionto neutralize impuritiesA in the silk, for if the silk should happen tocontain impurities having acid reactions, an alkaline neutralizingagent, such as sodium phosphate, or other weakly ionizable alkalinematerial, or ammonium` hydroxide, may be employed for this purpose.

The methods embodying the invention are also not limited to their usewith the particular type o! apparatus described hereinabove, for otherapparatus may be used with comparable results. For instance, instead ofemploying a Franklin dyeing machine to practice the invention, theapparatus known as the "Theis dyeing machine and "Obermaier ldyeingmachine, which work on a similar principle, may be employed.

As examples of the improvements which result from practicing the methodsembodying the invention, strands of No. 62 spun silk three quarters ofan-inch in length, which have been treated in accordance with theinvention, have a direct curf rent resistance of from 2000 to 3000kilomegohms at a relative humidity of 87.5% and a temperature commercialsilk have a direct current resistance of from 5 to '7 kilomegohms undersimilar conditions. Silk which has been treated with water alone inaccordance with the invention has a resistance of about 1000kilomegohms.

The curves' shown in Fig. 3 of the drawing also clearly illustrate theimprovements which result tained by employing a conductor 'which wasidentical in every respect with that employed in obtaining curve A,except that spun silk treated in accordance with the invention wasemployed to insulate the conductor. Curve D shows them. C. conductanceof the insulation in milimhos of a conductor at 1000 cyclesV per secondwhen insulated with commercial spun silk, while curve E shows the A. C.conductance of the insulation f of alike conductor insulated with spunsilk which vention.

The marked differences in the characteristics ot'silk which has beentreated in accordance with thev invention and silk which has not been sotreated are readily apparent from these curves. Itmayk be seen that asthe relative humidity increases the' A. C. capacity of a conductorinsulated with commercial spun silk increases rapidly, while the A. C.capacity of a similar conductor insulated with spun silk which has beentreated in accordance with the invention rises only a comparativelysmall amount and remains substantially constant. Similarly the A. C.conductance of the insulation of a conductor insulated with commercialsilk increases materially has been treated by methods embodying the inasthe relative humidity increases, but the A. C.

conductance of a similar'conductor insulated with treated silk remainssubstantially unchanged.

The comparative stability of the'v electrical characteristics ofinsulating silk which has been produced in accordance with the inventionrenders such silk especially useful in insulating conductors for use invarious types of electrical apparatus, particularly telephone apparatus.Since the currents employed in telephone circuits are alternativecurrents of audiofrequencies, and as the quality of transmission inthese circuits is inversely proportional to the A. C. conductancebetween adjacent insulated conductors, it may be readily seen thattransmisson of good quality may be obtained by employing a relativelysmall quantity of insulating silk embodying the invention; whereas, ifordinary commercial silk is employed a comparatively large quantity ofthe silk must be used in order to obtain comparable results.

For example, it has been found that. due to the improved properties ofinsulating silk embodying the invention, one type of insulated conductoremployed in telephone apparatus may be insulated with two servings ofthe improved silk, Whereas three servings are usually required when theordinary commercal silk is used, and in addition the conductors possesssatisfactory insulating properties with equal or better transmissioncharacteristics than heretofore obtained. In

vsome cases', it is possible to substitute silk mixed with cheapermaterials, such as cotton, for pure nil) , which comprises repeatedlysubjecting degummed silk to washing baths under pressure to removeionizable impurities from the silk, at least one of the baths includinga reagent capable of neutralizing impurities in the silk and theremaining baths comprising water.

2; The method of preparing insulating silk, which comprises repeatedlysubjecting degummed silkyto circulating washing baths under pressure Vtoremove ionizable impurities from the silk, at

least one ofwhich baths includes a volatile reagent capable ofneutralizing impurities in the silk and the remaining baths consistingof water.

3. The method of improving degummed insulating silk which comprisesrepeatedly washing the silk under pressure with a plurality ofcirculating washing baths toremove ionizable irnpurities from the silk,at least one'of which baths contains a fatty organic acid and theremaining baths consisting of water.

'4. The method of improving degammed insulating silk having an alkalinereaction, which comprises in circulating a dilute solution of' aceticacid through a mass of silk under pressure, and then circulating waterunder pressure through the silk until substantially all ionizablematerials are removed from the silk.

5. The method of Y preparing insulating silk, which consists in washingdegummed silk under pressure with a plurality of circulating washingbaths to remove the ionizable materials from the silk, at least one ofwhich baths other than the last one includes a reagent capable ofneutralizing impurities in the silk and the' remaining baths consistingof water, and drying the silk to remove substantially all of the washingiiuids therefrom.

6. As a new article of manufacture, electrical insulating materialcomprising-silk which is substantially free from ionizable impurities.

J7. The method of preparing insulating silk, which comprises repeatedlywashing degummed silk under pressure with a plurality of circulatingwashing baths to remove ionizable impurities from the silk, at least oneof which baths contains a weakly ionizable reagent capable oi.'Vneutralizing impurities in the silk and the remaining baths ,latingsilk, which comprises circulating through f,

a mass of the silk a reagent capable of neutralizing reagents employedin producing the degummed silk, and then circulating Water underpressure through the silk until substantially all ionizable substancesare removed from the silk.

9. As a new article of manufacture, insulating silkwhich isAsubstantially free from ionizable impurities and which has substantiallyconstant electrical characteristics under varying conditions of service.10. As a new article of manufacture, insulating silk Vcharacterized bybeing substantially free from ionizable impurities and by having adirect current resistance ofA at least 1000 kilomegohms per length ofthree-quarters of an inch at ST1/2% relative humidity and F.

11. The process of improving commercial degummed insulating silk, whichconsists in cirprises circulating a sodium phosphate solution culating avolatile reagent capable of neutralizing impurities in theA silk underpressure through a mass of the silk, washing the silk with water to'remove ionizable impurities therefrom, and heating the silk to removethe water and any remaining neutralizing reagent from the silk. Y

12. The process of improving commercial spun silk, which consists incirculating a hot solution of acetic acid through a mass ofthe silkunder pressure, circulating water under pressure through the silk toremove ionizable impurities therefrom, and heating the silk to removeVthe water and any remaining acid from the silk.

13. The method of improving commercial degummed tram silk. whichcomprises circulating an ammonia solution through a massof the silk, andWashing the silk with water to remove the ionizable materials therefrom.x

14 The method of improving commercial degummed tram silk, which consistsin circulating an ammonia solution through a mass of the silk, washingthe silk with water to remove the ionizable materials therefrom, andheating the silk to remove the water and any remaining ammonia from thesilk.

15. The method of improving commercial degummed insulating silk, whichcomprises circulating a neutralizing solution through a mass of thesilk, and circulatingwater through the silk to remove the ionizablematerialstherefrom.

16. The method of improving degummed insulating silk' having an alkalinereaction, which .comprises circulating a solution of a volatile acidthrough a mass of the silk, and washing the siik with water to removethe ionizable materials'no therefrom.l

1'7. The method of improving degummed insulating silk having an alkalinereaction, which comprises circulating a solution of a weakly ionizableacid through a mass of the silk, and washing the silk with water toremove the ionizable materials therefrom.

18. The method of improving degummed insulating silk having an alkalinereaction, which comprises circulating through a mass of the silk asolution of a compound falling within the empiricalv class of foi-mic,acetic, propionic, lactic, oxalic, tartaric, citric, carbonic and malicacids, and washing the silk with water to remove the ionizable materialstherefrom.

19. The method of improving degummedinsulating silk having an acidreaction, which. comprises circulating a solution of a volatile basicreagent through a mass of the silk, and washing the silk with water toremove the ionizable materials therefrom. v

20. The method of improving degummed insulating silk having an acidreaction, which comprises circulating a solution of a weakly ionizablebasic reagent through a mass of the silk, and

washingthe silk with water to remove the ionizable materials therefrom.

21. The method of improving degummed insulating silk having an acidreaction, which comthrough a mass of the silk, and washing the silk withwater to remove the ionizable materials therefrom.

22. The method of improvingtne. insulating lating silk having analkaline reaction which comprises neutralizing the free alkali in thesilk with a volatile organic acid and then circulating water through thesilk until substantially all the products of the neutralizing reactionand other ionizable materials are removed from the silk.

MARK C. LEWIS. ALGER M. LYNN.

